The present disclosure relates to a three-phase solid bowl screw centrifuge, or three-phase decanter having a rotatable drum, a screw arranged in the drum, a solid material discharge located at a first axial end of the drum, and two liquid outlets located at a second axial end of the drum. A first of the liquid outlets is for a lighter liquid phase and a second of the liquid outlets is for a heavier liquid phase. One of the liquid outlets includes a skimmer disk arranged in a skimmer chamber and the other of the liquid outlets is formed as an over flow. The present disclosure also relates to a method for operating or controlling the separating process by a centrifuge as just described.
With respect to the state of the art, the following documents are relevant: U.S. Pat. No. 3,623,656, International Patent Document WO 03/074 185 A1; German Patent Documents DE 195 00 600 C1, DE 102 23 802 A1, DE 38 22 983 A1; International Patent Document WO 02/062483 A1; and, German Patent Document DE 26 17 692 A1.
U.S. Pat. No. 3,623,656 shows a three-phase decanter by which two liquid phases and one solid phase can be discharged from the drum. When the machine is stopped, the liquid outlets can be adjusted by a conversion.
International Patent Document WO 03/074 185 A1 shows a three-phase decanter by which also two liquid phases and one solid phase can be discharged from the drum. The outflow quantity of the heavier liquid phase can be adjusted by a weir.
German Patent Document DE 38 22 983 A1 illustrates a three-phase decanter by which also two liquid phases and one solid phase can be discharged from the drum, one liquid phase being discharged through a weir and the other being discharged through a skimmer disk.
German Patent Documents DE 195 00 600 C1 and DE 102 23 802 A1 indicate two-phase decanters where the liquid is discharged by a skimmer disk, or centripetal, from a chamber.
International Patent Document WO 02/062483 A1 shows a method of operating a solid bowl screw centrifuge.
German Patent Document DE 26 17 692 A1 discloses a solid bowl screw centrifuge having several disk stacks consisting of separating disks and several screw areas.
In the case of three-phase separating decanters, as a rule, conversion parts are available for the adaptation to the respective product characteristics or for the adaptation of the process to the respective situations.
If, for example, during the process of obtaining olive oil in a three-phase operation, the product characteristics of the olive change from the start to the end of the harvest, it may be necessary to stop the processing, to remove the rotor and to install other regulating disks and/or regulating tubes. This is time-consuming and cost-intensive.
It has been suggested to regulate the heavier phase by a non-rotating throttle disk arranged outside the drum and to discharge the lighter phase by a skimmer disk, or centripetal pump. Although this construction has been successful, it requires at least the use of a displaceable throttle disk from a constructive point of view.
However, by varying the throttling at the skimmer disk, or centripetal pump, alone, the process cannot be sufficiently adjusted to the product characteristics, in order to avoid a conversion.
With respect to the above, the present disclosure relates to reducing the constructive expenditures for creating a three-phase decanter that is easily adaptable to changing product characteristics and of indicating an advantageous method for its operation.
The present disclosure relates to a three-phase solid bowl screw centrifuge comprised as follows.
A rotatable drum, a screw arranged in the drum, a solid material discharge located at a first axial end of the drum, and two liquid outlets located at a second axial end of the drum. A first of the liquid outlets is for a lighter liquid phase and a second of the liquid outlets is for a heavier liquid phase. One of the liquid outlets includes a skimmer disk arranged in a skimmer chamber and the other of the liquid outlets is formed as an overflow. Two regulating disks are located in front of the skimmer disk and extend radially from an outside of the drum toward an inside of the drum. A siphon disk extends between the regulating disks and into the skimmer chamber from an interior circumference of the skimmer chamber to an exterior circumference of the skimmer chamber. An annular chamber is formed during an operation and is located between the siphon disk and the skimmer disk. The siphon disk and skimmer disk act as axial boundaries for an axial area, and the annular chamber is further located between an inside radius of the lighter liquid phase in the axial area and an inner wall of the skimmer chamber in the axial area. A fluid feed pipe leads into the annular chamber to change a pressure on the annular chamber and to change at least one of a separation zone between the lighter and heavier phases and/or a pool depth in the drum. A feed pipe and a removal pipe for feeding fluid to the chamber and removing it from the chamber may also be provided.
As a result of a change of pressure in the annular chamber, as required, in connection with a throttling effect onto the skimmer disk, or centripetal pump, the separating zone in the drum can easily be shifted, which also results in a change of the liquid level. A conversion, which would otherwise be required as a result of changes of the characteristics of the product, as a rule, can be eliminated by utilizing the given regulating range. The constructive expenditures for providing the annular chamber are low.
As suggested above, the annular chamber, preferably, has a fluid pipe for feeding a fluid, particularly a gas, into the annular chamber, as a device for changing the pressure in the annular chamber.
The overflow for the other phase can be implemented by radial discharge pipes, which penetrate the drum shell or the drum lid.
This basic construction can be implemented particularly in two variants. In one variant, the heavier liquid phase is discharged through the discharge pipe and the lighter liquid phase is discharged through the skimmer disk, or centripetal pump. In the other variant, the lighter liquid phase is discharged through the discharge pipe and the heavier liquid phase is discharged through the skimmer disk. Both variants permit a good controlling of the process but result in different regulating characteristics.
The present disclosure also relates to a process for operating a three-phase solid bowl screw centrifuge. The regulating of the separating operation in the drum takes place in a very simple manner by changing the pressure in the annular chamber as the manipulated variable. This variant may be preferred because a simple and good regulating of the separating operation becomes possible.
As an alternative, it is also conceivable that the regulating of the separating operation in the drum takes place by changing the rotational speed of the drum as the manipulated variable.
The regulating of the separating operation in the drum may also take place as a function of the concentration in the solid phase or in one or both discharged liquid phases as the controlled variable.
The embodiments of the present disclosure are also suitable for the phase separation when obtaining hydrometals, such as cobalt, nickel, copper.
When obtaining hydrometals, such as cobalt, nickel, copper, the emulsion formation cannot be avoided during the extraction. The extraction, as well as the emulsion, includes three phases: an organic phase; an aqueous phase; and a solids phase. The open sedimentation tanks of the extraction are susceptible to contamination from the air. These different dust concentrations lead to a density difference of the individual phases in the emulsion. The decanter, according to the present disclosure, provides a remedy.
In order to meet these dynamic process demands, the separating diameter within the decanter can be adapted on-line by an increase of pressure into the annular chamber. As a result, the emulsion is cleanly separated into three phases. The use of a centrifuge according to the present disclosure for the emulsion separation when obtaining hydrometals, such as cobalt, nickel, copper, therefore offers considerable advantages.
Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings.